/*

 * Copyright (c) 2015, 2018, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

import java.io.Closeable;

import java.io.IOException;

import java.lang.System.Logger.Level;

import java.net.InetSocketAddress;

import java.nio.ByteBuffer;

import java.nio.channels.SocketChannel;

import java.util.Arrays;

import java.util.IdentityHashMap;

import java.util.List;

import java.util.Map;

import java.util.TreeMap;

import java.util.concurrent.CompletableFuture;

import java.util.concurrent.CompletionStage;

import java.util.concurrent.ConcurrentLinkedDeque;

import java.util.concurrent.Flow;

import java.util.function.BiPredicate;

import java.util.function.Predicate;

import jdk.incubator.http.HttpClient.Version;

import jdk.incubator.http.internal.common.Demand;

import jdk.incubator.http.internal.common.FlowTube;

import jdk.incubator.http.internal.common.SequentialScheduler;

import jdk.incubator.http.internal.common.SequentialScheduler.DeferredCompleter;

import jdk.incubator.http.internal.common.Log;

import jdk.incubator.http.internal.common.Utils;

import static jdk.incubator.http.HttpClient.Version.HTTP_2;

/**

 * Wraps socket channel layer and takes care of SSL also.

 *

 * Subtypes are:

 *      PlainHttpConnection: regular direct TCP connection to server

 *      PlainProxyConnection: plain text proxy connection

 *      PlainTunnelingConnection: opens plain text (CONNECT) tunnel to server

 *      AsyncSSLConnection: TLS channel direct to server

 *      AsyncSSLTunnelConnection: TLS channel via (CONNECT) proxy tunnel

 */

abstract class HttpConnection implements Closeable {

    static final boolean DEBUG = Utils.DEBUG; // Revisit: temporary dev flag.

    final System.Logger  debug = Utils.getDebugLogger(this::dbgString, DEBUG);

    final static System.Logger DEBUG_LOGGER = Utils.getDebugLogger(

            () -> "HttpConnection(SocketTube(?))", DEBUG);

    /** The address this connection is connected to. Could be a server or a proxy. */

    final InetSocketAddress address;

    private final HttpClientImpl client;

    private final TrailingOperations trailingOperations;

    HttpConnection(InetSocketAddress address, HttpClientImpl client) {

        this.address = address;

        this.client = client;

        trailingOperations = new TrailingOperations();

    }

    private static final class TrailingOperations {

        private final Map<CompletionStage<?>, Boolean> operations =

                new IdentityHashMap<>();

        void add(CompletionStage<?> cf) {

            synchronized(operations) {

                cf.whenComplete((r,t)-> remove(cf));

                operations.put(cf, Boolean.TRUE);

            }

        }

        boolean remove(CompletionStage<?> cf) {

            synchronized(operations) {

                return operations.remove(cf);

            }

        }

    }

    final void addTrailingOperation(CompletionStage<?> cf) {

        trailingOperations.add(cf);

    }

//    final void removeTrailingOperation(CompletableFuture<?> cf) {

//        trailingOperations.remove(cf);

//    }

    final HttpClientImpl client() {

        return client;

    }

    //public abstract void connect() throws IOException, InterruptedException;

    public abstract CompletableFuture<Void> connectAsync();

    /** Tells whether, or not, this connection is connected to its destination. */

    abstract boolean connected();

    /** Tells whether, or not, this connection is secure ( over SSL ) */

    abstract boolean isSecure();

    /** Tells whether, or not, this connection is proxied. */

    abstract boolean isProxied();

    /** Tells whether, or not, this connection is open. */

    final boolean isOpen() {

        return channel().isOpen() &&

                (connected() ? !getConnectionFlow().isFinished() : true);

    }

    interface HttpPublisher extends FlowTube.TubePublisher {

        void enqueue(List<ByteBuffer> buffers) throws IOException;

        void enqueueUnordered(List<ByteBuffer> buffers) throws IOException;

        void signalEnqueued() throws IOException;

    }

    /**

     * Returns the HTTP publisher associated with this connection.  May be null

     * if invoked before connecting.

     */

    abstract HttpPublisher publisher();

    // HTTP/2 MUST use TLS version 1.2 or higher for HTTP/2 over TLS

    private static final Predicate<String> testRequiredHTTP2TLSVersion = proto ->

            proto.equals("TLSv1.2") || proto.equals("TLSv1.3");

   /**

    * Returns true if the given client's SSL parameter protocols contains at

    * least one TLS version that HTTP/2 requires.

    */

   private static final boolean hasRequiredHTTP2TLSVersion(HttpClient client) {

       String[] protos = client.sslParameters().getProtocols();

       if (protos != null) {

           return Arrays.stream(protos).filter(testRequiredHTTP2TLSVersion).findAny().isPresent();

       } else {

           return false;

       }

   }

    /**

     * Factory for retrieving HttpConnections. A connection can be retrieved

     * from the connection pool, or a new one created if none available.

     *

     * The given {@code addr} is the ultimate destination. Any proxies,

     * etc, are determined from the request. Returns a concrete instance which

     * is one of the following:

     *      {@link PlainHttpConnection}

     *      {@link PlainTunnelingConnection}

     *

     * The returned connection, if not from the connection pool, must have its,

     * connect() or connectAsync() method invoked, which ( when it completes

     * successfully ) renders the connection usable for requests.

     */

    public static HttpConnection getConnection(InetSocketAddress addr,

                                               HttpClientImpl client,

                                               HttpRequestImpl request,

                                               Version version) {

        HttpConnection c = null;

        InetSocketAddress proxy = request.proxy();

        if (proxy != null && proxy.isUnresolved()) {

            // The default proxy selector may select a proxy whose  address is

            // unresolved. We must resolve the address before connecting to it.

            proxy = new InetSocketAddress(proxy.getHostString(), proxy.getPort());

        }

        boolean secure = request.secure();

        ConnectionPool pool = client.connectionPool();

        if (!secure) {

            c = pool.getConnection(false, addr, proxy);

            if (c != null && c.isOpen() /* may have been eof/closed when in the pool */) {

                final HttpConnection conn = c;

                DEBUG_LOGGER.log(Level.DEBUG, () -> conn.getConnectionFlow()

                            + ": plain connection retrieved from HTTP/1.1 pool");

                return c;

            } else {

                return getPlainConnection(addr, proxy, request, client);

            }

        } else {  // secure

            if (version != HTTP_2) { // only HTTP/1.1 connections are in the pool

                c = pool.getConnection(true, addr, proxy);

            }

            if (c != null && c.isOpen()) {

                final HttpConnection conn = c;

                DEBUG_LOGGER.log(Level.DEBUG, () -> conn.getConnectionFlow()

                            + ": SSL connection retrieved from HTTP/1.1 pool");

                return c;

            } else {

                String[] alpn = null;

                if (version == HTTP_2 && hasRequiredHTTP2TLSVersion(client)) {

                    alpn = new String[] { "h2", "http/1.1" };

                }

                return getSSLConnection(addr, proxy, alpn, request, client);

            }

        }

    }

    private static HttpConnection getSSLConnection(InetSocketAddress addr,

                                                   InetSocketAddress proxy,

                                                   String[] alpn,

                                                   HttpRequestImpl request,

                                                   HttpClientImpl client) {

        if (proxy != null)

            return new AsyncSSLTunnelConnection(addr, client, alpn, proxy,

                                                proxyTunnelHeaders(request));

        else

            return new AsyncSSLConnection(addr, client, alpn);

    }

    /**

     * This method is used to build a filter that will accept or

     * veto (header-name, value) tuple for transmission on the

     * wire.

     * The filter is applied to the headers when sending the headers

     * to the remote party.

     * Which tuple is accepted/vetoed depends on:

     * <pre>

     *    - whether the connection is a tunnel connection

     *      [talking to a server through a proxy tunnel]

     *    - whether the method is CONNECT

     *      [establishing a CONNECT tunnel through a proxy]

     *    - whether the request is using a proxy

     *      (and the connection is not a tunnel)

     *      [talking to a server through a proxy]

     *    - whether the request is a direct connection to

     *      a server (no tunnel, no proxy).

     * </pre>

     * @param request

     * @return

     */

    BiPredicate<String,List<String>> headerFilter(HttpRequestImpl request) {

        if (isTunnel()) {

            // talking to a server through a proxy tunnel

            // don't send proxy-* headers to a plain server

            assert !request.isConnect();

            return Utils.NO_PROXY_HEADERS_FILTER;

        } else if (request.isConnect()) {

            // establishing a proxy tunnel

            // check for proxy tunnel disabled schemes

            // assert !this.isTunnel();

            assert request.proxy() == null;

            return Utils.PROXY_TUNNEL_FILTER;

        } else if (request.proxy() != null) {

            // talking to a server through a proxy (no tunnel)

            // check for proxy disabled schemes

            // assert !isTunnel() && !request.isConnect();

            return Utils.PROXY_FILTER;

        } else {

            // talking to a server directly (no tunnel, no proxy)

            // don't send proxy-* headers to a plain server

            // assert request.proxy() == null && !request.isConnect();

            return Utils.NO_PROXY_HEADERS_FILTER;

        }

    }

    // Composes a new immutable HttpHeaders that combines the

    // user and system header but only keeps those headers that

    // start with "proxy-"

    private static HttpHeaders proxyTunnelHeaders(HttpRequestImpl request) {

        Map<String, List<String>> combined = new TreeMap<>(String.CASE_INSENSITIVE_ORDER);

        combined.putAll(request.getSystemHeaders().map());

        combined.putAll(request.headers().map()); // let user override system

        // keep only proxy-* - and also strip authorization headers

        // for disabled schemes

        return ImmutableHeaders.of(combined, Utils.PROXY_TUNNEL_FILTER);

    }

    /* Returns either a plain HTTP connection or a plain tunnelling connection

     * for proxied WebSocket */

    private static HttpConnection getPlainConnection(InetSocketAddress addr,

                                                     InetSocketAddress proxy,

                                                     HttpRequestImpl request,

                                                     HttpClientImpl client) {

        if (request.isWebSocket() && proxy != null)

            return new PlainTunnelingConnection(addr, proxy, client,

                                                proxyTunnelHeaders(request));

        if (proxy == null)

            return new PlainHttpConnection(addr, client);

        else

            return new PlainProxyConnection(proxy, client);

    }

    void closeOrReturnToCache(HttpHeaders hdrs) {

        if (hdrs == null) {

            // the connection was closed by server, eof

            close();

            return;

        }

        if (!isOpen()) {

            return;

        }

        HttpClientImpl client = client();

        if (client == null) {

            close();

            return;

        }

        ConnectionPool pool = client.connectionPool();

        boolean keepAlive = hdrs.firstValue("Connection")

                .map((s) -> !s.equalsIgnoreCase("close"))

                .orElse(true);

        if (keepAlive) {

            Log.logTrace("Returning connection to the pool: {0}", this);

            pool.returnToPool(this);

        } else {

            close();

        }

    }

    /* Tells whether or not this connection is a tunnel through a proxy */

    boolean isTunnel() { return false; }

    abstract SocketChannel channel();

    final InetSocketAddress address() {

        return address;

    }

    abstract ConnectionPool.CacheKey cacheKey();

    /**

     * Closes this connection, by returning the socket to its connection pool.

     */

    @Override

    public abstract void close();

    abstract void shutdownInput() throws IOException;

    abstract void shutdownOutput() throws IOException;

    // Support for WebSocket/RawChannelImpl which unfortunately

    // still depends on synchronous read/writes.

    // It should be removed when RawChannelImpl moves to using asynchronous APIs.

    abstract static class DetachedConnectionChannel implements Closeable {

        DetachedConnectionChannel() {}

        abstract SocketChannel channel();

        abstract long write(ByteBuffer[] buffers, int start, int number)

                throws IOException;

        abstract void shutdownInput() throws IOException;

        abstract void shutdownOutput() throws IOException;

        abstract ByteBuffer read() throws IOException;

        @Override

        public abstract void close();

        @Override

        public String toString() {

            return this.getClass().getSimpleName() + ": " + channel().toString();

        }

    }

    // Support for WebSocket/RawChannelImpl which unfortunately

    // still depends on synchronous read/writes.

    // It should be removed when RawChannelImpl moves to using asynchronous APIs.

    abstract DetachedConnectionChannel detachChannel();

    abstract FlowTube getConnectionFlow();

    /**

     * A publisher that makes it possible to publish (write)

     * ordered (normal priority) and unordered (high priority)

     * buffers downstream.

     */

    final class PlainHttpPublisher implements HttpPublisher {

        final Object reading;

        PlainHttpPublisher() {

            this(new Object());

        }

        PlainHttpPublisher(Object readingLock) {

            this.reading = readingLock;

        }

        final ConcurrentLinkedDeque<List<ByteBuffer>> queue = new ConcurrentLinkedDeque<>();

        volatile Flow.Subscriber<? super List<ByteBuffer>> subscriber;

        volatile HttpWriteSubscription subscription;

        final SequentialScheduler writeScheduler =

                    new SequentialScheduler(this::flushTask);

        @Override

        public void subscribe(Flow.Subscriber<? super List<ByteBuffer>> subscriber) {

            synchronized (reading) {

                //assert this.subscription == null;

                //assert this.subscriber == null;

                if (subscription == null) {

                    subscription = new HttpWriteSubscription();

                }

                this.subscriber = subscriber;

            }

            // TODO: should we do this in the flow?

            subscriber.onSubscribe(subscription);

            signal();

        }

        void flushTask(DeferredCompleter completer) {

            try {

                HttpWriteSubscription sub = subscription;

                if (sub != null) sub.flush();

            } finally {

                completer.complete();

            }

        }

        void signal() {

            writeScheduler.runOrSchedule();

        }

        final class HttpWriteSubscription implements Flow.Subscription {

            final Demand demand = new Demand();

            @Override

            public void request(long n) {

                if (n <= 0) throw new IllegalArgumentException("non-positive request");

                demand.increase(n);

                debug.log(Level.DEBUG, () -> "HttpPublisher: got request of "

                            + n + " from "

                            + getConnectionFlow());

                writeScheduler.runOrSchedule();

            }

            @Override

            public void cancel() {

                debug.log(Level.DEBUG, () -> "HttpPublisher: cancelled by "

                          + getConnectionFlow());

            }

            void flush() {

                while (!queue.isEmpty() && demand.tryDecrement()) {

                    List<ByteBuffer> elem = queue.poll();

                    debug.log(Level.DEBUG, () -> "HttpPublisher: sending "

                                + Utils.remaining(elem) + " bytes ("

                                + elem.size() + " buffers) to "

                                + getConnectionFlow());

                    subscriber.onNext(elem);

                }

            }

        }

        @Override

        public void enqueue(List<ByteBuffer> buffers) throws IOException {

            queue.add(buffers);

            int bytes = buffers.stream().mapToInt(ByteBuffer::remaining).sum();

            debug.log(Level.DEBUG, "added %d bytes to the write queue", bytes);

        }

        @Override

        public void enqueueUnordered(List<ByteBuffer> buffers) throws IOException {

            // Unordered frames are sent before existing frames.

            int bytes = buffers.stream().mapToInt(ByteBuffer::remaining).sum();

            queue.addFirst(buffers);

            debug.log(Level.DEBUG, "inserted %d bytes in the write queue", bytes);

        }

        @Override

        public void signalEnqueued() throws IOException {

            debug.log(Level.DEBUG, "signalling the publisher of the write queue");

            signal();

        }

    }

    String dbgTag = null;

    final String dbgString() {

        FlowTube flow = getConnectionFlow();

        String tag = dbgTag;

        if (tag == null && flow != null) {

            dbgTag = tag = this.getClass().getSimpleName() + "(" + flow + ")";

        } else if (tag == null) {

            tag = this.getClass().getSimpleName() + "(?)";

        }

        return tag;

    }

    @Override

    public String toString() {

        return "HttpConnection: " + channel().toString();

    }

}